Messages in this thread | | | Date | Tue, 16 Feb 2016 19:35:18 +1100 | From | Dave Chinner <> | Subject | Re: [PATCH] kernel: fs: drop_caches: add dds drop_caches_count |
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On Mon, Feb 15, 2016 at 11:14:13PM -0800, Nag Avadhanam wrote: > On Mon, 15 Feb 2016, Dave Chinner wrote: > > >On Tue, Feb 16, 2016 at 02:58:04AM +0000, Nag Avadhanam (nag) wrote: > >>Its the calculation of the # of bytes of non-reclaimable file system cache > >>pages that has been troubling us. We do not want to count inactive file > >>pages (of programs/binaries) that were once mapped by any process in the > >>system as reclaimable because that might lead to thrashing under memory > >>pressure (we want to alert admins before system starts dropping text > >>pages). > > > >The code presented does not match your requirements. It only counts > >pages that are currently mapped into ptes. hence it will tell you > >that once-used and now unmapped binary pages are reclaimable, and > >drop caches will reclaim them. hence they'll need to be fetched from > >disk again if they are faulted in again after a drop_caches run. > > Will the inactive binary pages be automatically unmapped even if the process > into whose address space they are mapped is still around? I thought they > are left mapped until such time there is memory pressure.
Right, page reclaim via memory pressure can unmap mapped pages in order to reclaim them. Drop caches will skip them.
> We only care for binary pages (active and inactive) mapped into the > address spaces of live processes. Its okay to aggressively reclaim > inactive > pages once mapped into processes that are no longer around.
Ok, if you're only concerned about live processes then drop caches should behave as you want.
Cheers,
Dave.
-- Dave Chinner david@fromorbit.com
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